1. Field of the Invention
The present invention relates to an image pickup apparatus and, more particularly, to an image pickup apparatus that combines electronic zooming and optical zooming.
2. Description of the Related Art
A variety of image pickup apparatuses that photoelectrically convert the image of a subject image into a video signal through an image pickup device have been proposed. The image pickup apparatuses find widespread use ranging from digital cameras and video cameras to the one for picking up an image observed by a microscope, and to the one for picking up an image viewed through an endoscope.
The images picked up by such an image pickup apparatus are chiefly categorized into two types, namely, still pictures and moving pictures. Still pictures are obtained by taking one frame of video data only and moving pictures are obtained by successively taking a plurality of frames of picture data. Electronic cameras proposed take both a still picture and a moving picture.
The electronic cameras today have a number of pixels as many as several millions, for example, and take a high-definition still picture. In the meantime, when a moving picture is handled, such a camera displays a picture on a display element of several tens of thousands to several hundreds of thousands of pixels or sometimes stores the moving picture together with the still picture in a storage medium with a limited storage capacity. Therefore, an electronic camera having a resolution of several hundreds of thousands of pixels works enough for taking such pictures.
Pixel information read from an image pickup device is thus skip-read out or interpolated to create image data for use as a moving picture.
An image pickup apparatus such as the electronic camera incorporates an optical zoom which varies the size of the image of a subject focused on the image pickup device using an optical system having a variable focal length, and an electronic zoom which varies an output angle of field of a picture signal which is consequently output by clipping a image formed on the image pickup device.
One image pickup apparatus having an electronic zoom is disclosed in Japanese Unexamined Patent Application Publication No. 2000-295530. The disclosed image pickup apparatus is a solid-state image pickup apparatus having two-dimensionally arranged, photoelectrical converter elements, which are accessed in a random fashion during operation. The image pickup apparatus includes a first skipping unit for reading data of any designated pixels, and a second skipping unit for reading data of an area of pixels smaller than the picture frame read by the first skipping unit. The pixels read by the first skipping unit and the pixels read by the second skipping unit are equalized.
Another image pickup apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 10-42183. The disclosed image pickup apparatus includes a first adjusting unit for optically adjusting the angle of view of an image, a second adjusting unit for electronically adjusting the angle of view of the image, and a controller for determining the angle of view by controlling the first adjusting unit and the second adjusting unit. The controller controls the angle of view to an angle of view desired by a user through the second adjusting unit, and then transfers control of the angle of view to the first adjusting unit from the second adjusting unit while keeping the angle of view. The disclosed image pickup apparatus employs a CCD (Charge-Coupled Device). During an electronic zooming operation, the image pickup apparatus reads data of all pixels using the CCD and stores data in a frame memory, and then electronically interpolates the data in accordance with a pixel signal of a smaller number of pixels contained in an area within the entire angle of view, thereby resulting in an output image having a desired angle view.
Japanese Unexamined Patent Application Publication No. 5-232372 discloses a camera having a line-of-sight detector. The disclosed camera includes a light projector for projecting luminous fluxes in a plurality of directions, a range finder including a photoreceiver for receiving light rays reflected from subject images to which the luminous fluxes are projected, and for outputting a signal into which the received light rays are photoelectrically converted, the range finder thus range finding a plurality of range finding areas based on the photoelectrical output signal, a line-of-sight detector for detecting the line of sight of a photographer to determine what direction the photographer looks to in the range finder, and a lens controller for controlling a photographing lens based on the output of the range finder in accordance with the sight line provided by the line-of-sight detector. During a light projection operation by the light projector, the line-of-sight detector detects the line of sight of the photographer in the directions in which light is projected.
In the image pickup apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-295530, the electronic zooming is performed by varying a skip amount during reading, and discontinuous electronic zooming only is possible. The angle of view cannot be varied in steps of angles finer than the skip amount. The electronic zoom is unable to cover the angle of view in excess of a field of view taken by the image pickup device because the image focused on the image pickup device is clipped.
In the image pickup apparatus disclosed in Japanese Unexamined Patent Application Publication 10-42183, all pixels data needs first to be read using the CCD image pickup device. A high-rate clock corresponding to the number of pixels is thus supplied to the device. To skip-read out the data, information of all pixels needs to be stored into a frame memory. The use of the frame memory gives rise to an increase in cost. Since an interpolation processing is electronically performed on the picture signal based on a small number of pixels, image quality is degraded more as an image is expanded more. The disclosed image pickup apparatus cannot tell whether a subject observed by the user falls within a range by the electronic zoom or a range by the optical zoom, and thus does not provide any indication to discriminate between the range covered by the electronic zoom and the range covered by the optical zoom. Furthermore, since the image pickup apparatus is not provided with any particular switch to switch between the electronic zoom and the optical zoom, the user has no option to select between the electronic zoom and the optical zoom. Even if the user attempts to record a high-definition still picture without using the electronic zoom, the user cannot operate it. No consideration is given to a still picture recording mode intended to take a high-definition still picture.
Japanese Unexamined Patent Application Publication No. 5-232372 further discloses a technique in which the focal length of the imaging lens is modified in response to the detection of the line of sight. No particular consideration is given to the zooming of the photographing lens and the selection between the optical zoom and the electronic zoom.